1. Field of the Invention
The present invention relates to electronic safety devices, and more particularly to devices for initiating protective action in response to current variations indicative of the existence of unsafe conditions, such as the inadvertent driving of a power-operated gate against a vehicle or a human being.
2. Prior Art Statement
(The following prior art is disclosed pursuant to 37 CFR 1.56, 1.97, and 1.98.)
U.S. Pat. No. 3,959,704, issued May 25, 1976, teaches the concept of providing time delay means for determining when a run overload protective circuit is to be activated after startup of a motor. A motor current sensing transformer is used to provide the motor condition signal for the patented device. FIG. 1 shows delay means 112 which inhibits operation of the patented circuit during the starting surge of the motor current, as taught at column 6, line 25 et seq.
U.S. Pat. No. 3,435,289, issued Mar. 25, 1969, discloses an automatic disconnect device for an electrical motor responsive to the sensing of a variation in motor current level. Other United States patents which were adduced by a preliminary patentability search of the present invention, and thus might be held to have some relation to the present invention, are U.S. Pat. Nos. 4,057,842; 4,000,446; 3,953,777; 3,602,771; 4,041,540; and 4,060,844.
It is to be particularly noted that while some of the abovecited prior patents relate to the protection of electric motors from the consequences of overload, the devices disclosed therein are not necessarily sufficiently sensitive or rapid-acting for use in the protection of vehicles or human beings from impingent, motordriven gates and the like.